SSM2301

Preliminary Technical Data

LAYOUT

As output power continues to increase, care needs to be taken to

lay out PCB traces and wires properly between the amplifier,

load, and power supply. A good practice is to use short, wide

PCB tracks to decrease voltage drops and minimize inductance.

Make track widths at least 200 mil for every inch of track length

for lowest DCR, and use 1 oz or 2 oz of copper PCB traces to

further reduce IR drops and inductance. A poor layout

increases voltage drops, consequently affecting efficiency. Use

large traces for the power supply inputs and amplifier outputs to

minimize losses due to parasitic trace resistance. Proper

grounding guidelines help to improve audio performance,

minimize crosstalk between channels, and prevent switching

noise from coupling into the audio signal. To maintain high

output swing and high peak output power, the PCB traces that

connect the output pins to the load and supply pins should be as

wide as possible to maintain the minimum trace resistances. It

is also recommended to use a large-area ground plane for

minimum impedances. Good PCB layouts also isolate critical

analog paths from sources of high interference. High frequency

circuits (analog and digital) should be separated from low

frequency ones. Properly designed multilayer printed circuit

boards can reduce EMI emission and increase immunity to RF

field by a factor of 10 or more compared with double-sided

boards. A multilayer board allows a complete layer to be used

for ground plane, whereas the ground plane side of a double-

side board is often disrupted with signal crossover. If the system

has separate analog and digital ground and power planes, the

analog ground plane should be underneath the analog power

plane, and, similarly, the digital ground plane should be

underneath the digital power plane. There should be no overlap

between analog and digital ground planes nor analog and

digital power planes.

INPUT CAPACITOR SELECTION

The SSM2301 will not require input coupling capacitors if the

capacitors are required if the input signal is not biased within

this recommended input dc common-mode voltage range, if

high-pass filtering is needed (Figure 19), or if using a single-

ended source (Figure 20). If high-pass filtering is needed at the

input, the input capacitor along with the input resistor of the

SSM2301 will form a high-pass filter whose corner frequency is

determined by the following equation:

Input capacitor can have very important effects on the circuit

performance. Not using input capacitors degrades the output

offset of the amplifier as well as the PSRR performance.

PROPER POWER SUPPLY DECOUPLING

To ensure high efficiency, low total harmonic distortion (THD),

and high PSRR, proper power supply decoupling is necessary.

Noise transients on the power supply lines are short-duration

voltage spikes. Although the actual switching frequency can

range from 10 kHz to 100 kHz, these spikes can contain

frequency components that extend into the hundreds of

megahertz. The power supply input needs to be decoupled with

a good quality low ESL and low ESR capacitor—usually around

4.7 μF. This capacitor bypasses low frequency noises to the

ground plane. For high frequency transients noises, use a 0.1 μF

capacitor as close as possible to the VDD pin of the device.

Placing the decoupling capacitor as close as possible to the

SSM2301 helps maintain efficiency performance.

Rev. PrH | Page 12 of 19